Method and device for removing self-interference signal in environment using fdr mode

ABSTRACT

A method for removing a self-interference signal by a device supporting an FDR mode can further comprise the steps of: transmitting a signal to a counterpart node in a predetermined time interval; generating, in an RF stage of the device, a residual self-interference signal after removal of an analog self-interference signal with respect to the signal and then storing same; and receiving from the counterpart node an ACK/NACK signal with respect to the transmission of the signal; and determining whether or not the stored residual self-interference signal is to be used thereafter on the basis of the ACK/NACK signal.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method for performing self-interference signalcancellation in an environment using an FDR scheme and device therefor.

BACKGROUND ART

Compared to conventional half duplex communication in which time orfrequency resources are divided orthogonally, full duplex communicationdoubles a system capacity in theory by allowing a node to performtransmission and reception simultaneously.

FIG. 1 is a conceptual view of a UE and a Base Station (BS) whichsupport Full Duplex Radio (FDR).

In the FDR situation illustrated in FIG. 1, the following three types ofinterference are produced.

Intra-device self-interference: Because transmission and reception takeplace in the same time and frequency resources, a desired signal and asignal transmitted from a BS or UE are received at the same time at theBS or UE. The transmitted signal is received with almost no attenuationat a Reception (Rx) antenna of the BS or UE, and thus with much largerpower than the desired signal. As a result, the transmitted signalserves as interference.

UE to UE inter-link interference: An Uplink (UL) signal transmitted by aUE is received at an adjacent UE and thus serves as interference.

BS to BS inter-link interference: The BS to BS inter-link interferencerefers to interference caused by signals that are transmitted betweenBSs or heterogeneous BSs (pico, femto, and relay) in a HetNet state andreceived by an Rx antenna of another BS.

Among the tree types of interference, the intra-device self-interference(hereinafter referred to as self-interference (SI)) occurs only in theFDR system and it may result in performance degradation in the FDRsystem. Therefore, the SI is considered as a main problem for efficientoperation of the FDR system.

DISCLOSURE OF THE INVENTION Technical Task

An object of the present invention is to provide a method performed by adevice supporting an FDR scheme for self-interference signalcancellation.

Another object of the present invention is to provide a device for notonly supporting the FDR scheme but also performing the self-interferencesignal cancellation.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description.

Technical Solutions

In an aspect of the present invention, provided herein is a method forperforming self-interference signal cancellation, the method performedby an apparatus supporting a full duplex communication (FDR) mode andincluding: transmitting a signal to a target node in a predeterminedtime interval; generating and storing a residual self-interferencesignal after cancelling an analog self-interference signal with respectto the signal at a radio frequency (RF) end of the device; receiving anacknowledgement/negative-acknowledgement (ACK/NACK) signal from thetarget node in response to the transmitted signal; and determiningwhether to use the stored residual self-interference signal later basedon the ACK/NACK signal. When an ACK signal is received from the targetnode in response to the transmitted signal, the method may furtherinclude determining to discard the stored self-interference signal. Onthe other hand, when a NACK signal is received from the target node inresponse to the transmitted signal, the method may further includedetermining whether a signal received in the predetermined time intervalis successfully decoded. In addition, the method may further include:retransmitting the signal to the target node; and when the signalreceived in the predetermined time interval is successfully decoded,using the stored residual self-interference signal in cancelling adigital self-interference signal associated with the retransmission.Moreover, the method may further include: retransmitting the signal tothe target node; and when the signal received in the predetermined timeinterval is not successfully decoded, determining whetherself-interference cancellation is successful. In this case, the successor failure of the self-interference cancellation may be determined basedon whether a predetermined number or more of consecutive ACK signals arereceived from the target node. Furthermore, when it is determined thatthe self-interference cancellation is successful, the method may furtherinclude using the stored residual self-interference signal in cancellinga digital self-interference signal associated with the retransmission.On the contrary, when it is determined that the self-interferencecancellation is not successful, the method may further includediscarding the stored residual self-interference signal.

In another aspect of the present invention, provided herein is anapparatus performing self-interference signal cancellation, theapparatus supporting a full duplex communication (FDR) mode, theapparatus comprising: a transmitted configured to transmit a signal to atarget node in a predetermined time interval; a radio frequency (RF)unit configured to generate and store a residual self-interferencesignal after cancelling an analog self-interference signal with respectto the signal; a receiver configured to receive anacknowledgement/negative-acknowledgement (ACK/NACK) signal from thetarget node in response to the transmitted signal; and a processorconfigured to determine whether to use the stored residualself-interference signal later based on the ACK/NACK signal. When an ACKsignal is received from the target node in response to the transmittedsignal, the processor may be configured to determine to discard thestored self-interference signal. On the other hand, when the receiverreceives a NACK signal from the target node in response to thetransmitted signal, the processor may be configured to determine whethera signal received in the predetermined time interval is successfullydecoded. In addition, the transmitter may be configured to retransmitthe signal to the target node. When the signal received in thepredetermined time interval is successfully decoded, the RF unit may beconfigured to use the stored residual self-interference signal incancelling a digital self-interference signal associated with theretransmission.

In the device, the transmitter may be configured to retransmit thesignal to the target node. When the signal received in the predeterminedtime interval is not successfully decoded, the processor may beconfigured to determine whether self-interference cancellation issuccessful. In addition, the processor may be configured to determinethe success or failure of the self-interference cancellation based onwhether a predetermined number or more of consecutive ACK signals arereceived from the target node. Moreover, when it is determined that theself-interference cancellation is successful, the RF unit may beconfigured to use the stored residual self-interference signal incancelling a digital self-interference signal for the retransmission. Onthe contrary, when it is determined that the self-interferencecancellation is not successful, the processor may be configured todiscard the stored residual self-interference signal.

Advantageous Effects

According to various embodiments of the present invention,self-interference cancellation complexity can be significantly reduced,thereby improving communication performance of the FDR scheme.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved through the present invention are not limited towhat has been particularly described hereinabove and other advantages ofthe present invention will be more clearly understood from the followingdetailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a diagram illustrating an exemplary network supportingfull-duplex/half-duplex radio modes of a user equipment according to thepresent invention.

FIG. 2 is a block diagram illustrating configurations of a base station105 and a user equipment 110 in a wireless communication system 100.

FIG. 3 is a conceptual diagram of self-interference (SI) and Tx/Rx linksin an FDR communication environment.

FIG. 4 is a diagram illustrating positions within an RF transceiver (orRF front end) of a device to which three types of interferencecancellation schemes are applied.

FIG. 5 is a block diagram of a self-interference cancellation (Self-IC)device included in a communication device available in an OFDM-basedcommunication system environment in accordance with FIG. 4.

FIG. 6 is a diagram illustrating a procedure for self-interferencecancellation performed by devices (e.g., user equipment, base station,etc.) in the FDR system.

FIG. 7 is a diagram illustrating another procedure for self-interferencecancellation (Self-IC) different from that of FIG. 6.

FIG. 8 is a diagram illustrating a particular procedure for regeneratinga digital SI signal and storing the digital SI signal in a memory unitbased on three cases shown in Table 2.

FIG. 9 is a diagram for explaining a procedure for self-interferencecancellation proposed in the present invention.

FIG. 10 is a block diagram of a device for performing the proposedmethod based on FIG. 5.

FIG. 11 illustrates an example in which success of self-interferencecancellation (Self-IC) is expected based on consecutive HI informationin accordance with embodiment 5-1.

FIG. 12 illustrates an example in which failure of self-interferencecancellation (Self-IC) is expected based on consecutive HI informationin accordance with embodiment 5-1.

FIG. 13 illustrates an example in which success of self-interferencecancellation (Self-IC) is expected based on consecutive HI informationin accordance with embodiment 5-2.

FIG. 14 illustrates an example in which failure of self-interferencecancellation (Self-IC) is expected based on consecutive HI informationin accordance with embodiment 5-2.

FIG. 15 illustrates an example in which success of self-interferencecancellation (Self-IC) is expected based on consecutive HI informationin accordance with embodiment 5-3.

FIG. 16 illustrates an example in which failure of self-interferencecancellation (Self-IC) is expected based on consecutive HI informationin accordance with embodiment 5-3.

BEST MODE FOR INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. In the following detailed description of the inventionincludes details to help the full understanding of the presentinvention. Yet, it is apparent to those skilled in the art that thepresent invention can be implemented without these details. Forinstance, although the following descriptions are made in detail on theassumption that a mobile communication system includes 3GPP LTE system,the following descriptions are applicable to other random mobilecommunication systems in a manner of excluding unique features of the3GPP LTE.

Occasionally, to prevent the present invention from getting vaguer,structures and/or devices known to the public are skipped or can berepresented as block diagrams centering on the core functions of thestructures and/or devices. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Besides, in the following description, assume that a terminal is acommon name of such a mobile or fixed user stage device as a userequipment (UE), a mobile station (MS), an advanced mobile station (AMS)and the like. And, assume that a base station (BS) is a common name ofsuch a random node of a network stage communicating with a terminal as aNode B (NB), an eNode B (eNB), an access point (AP) and the like.Although the present specification is described based on IEEE 802.16msystem, contents of the present invention may be applicable to variouskinds of other communication systems.

In a mobile communication system, a user equipment is able to receiveinformation in downlink and is able to transmit information in uplink aswell. Information transmitted or received by the user equipment node mayinclude various kinds of data and control information. In accordancewith types and usages of the information transmitted or received by theuser equipment, various physical channels may exist.

The following descriptions are usable for various wireless accesssystems including CDMA (code division multiple access), FDMA (frequencydivision multiple access), TDMA (time division multiple access), OFDMA(orthogonal frequency division multiple access), SC-FDMA (single carrierfrequency division multiple access) and the like. CDMA can beimplemented by such a radio technology as UTRA (universal terrestrialradio access), CDMA 2000 and the like. TDMA can be implemented with sucha radio technology as GSM/GPRS/EDGE (Global System for Mobilecommunications)/General Packet Radio Service/Enhanced Data Rates for GSMEvolution). OFDMA can be implemented with such a radio technology asIEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, E-UTRA (EvolvedUTRA), etc. UTRA is a part of UMTS (Universal Mobile TelecommunicationsSystem). 3GPP (3rd Generation Partnership Project) LTE (long termevolution) is a part of E-UMTS (Evolved UMTS) that uses E-UTRA. The 3GPPLTE employs OFDMA in DL and SC-FDMA in UL. And, LTE-A (LTE-Advanced) isan evolved version of 3GPP LTE.

Moreover, in the following description, specific terminologies areprovided to help the understanding of the present invention. And, theuse of the specific terminology can be modified into another form withinthe scope of the technical idea of the present invention.

FIG. 2 is a block diagram for configurations of a base station 105 and auser equipment 110 in a wireless communication system 100.

Although one base station 105 and one user equipment 110 (D2D userequipment included) are shown in the drawing to schematically representa wireless communication system 100, the wireless communication system100 may include at least one base station and/or at least one userequipment.

Referring to FIG. 2, a base station 105 may include a transmitted (Tx)data processor 115, a symbol modulator 120, a transmitter 125, atransceiving antenna 130, a processor 180, a memory 185, a receiver 190,a symbol demodulator 195 and a received data processor 197. And, a userequipment 110 may include a transmitted (Tx) data processor 165, asymbol modulator 170, a transmitter 175, a transceiving antenna 135, aprocessor 155, a memory 160, a receiver 140, a symbol demodulator 155and a received data processor 150. Although the base station/userequipment 105/110 includes one antenna 130/135 in the drawing, each ofthe base station 105 and the user equipment 110 includes a plurality ofantennas. Therefore, each of the base station 105 and the user equipment110 of the present invention supports an MIMO (multiple input multipleoutput) system. And, the base station 105 according to the presentinvention may support both SU-MIMO (single user-MIMO) and MU-MIMO (multiuser-MIMO) systems.

In downlink, the transmitted data processor 115 receives traffic data,codes the received traffic data by formatting the received traffic data,interleaves the coded traffic data, modulates (or symbol maps) theinterleaved data, and then provides modulated symbols (data symbols).The symbol modulator 120 provides a stream of symbols by receiving andprocessing the data symbols and pilot symbols.

The symbol modulator 120 multiplexes the data and pilot symbols togetherand then transmits the multiplexed symbols to the transmitter 125. Indoing so, each of the transmitted symbols may include the data symbol,the pilot symbol or a signal value of zero. In each symbol duration,pilot symbols may be contiguously transmitted. In doing so, the pilotsymbols may include symbols of frequency division multiplexing (FDM),orthogonal frequency division multiplexing (OFDM), or code divisionmultiplexing (CDM).

The transmitter 125 receives the stream of the symbols, converts thereceived stream to at least one or more analog signals, additionallyadjusts the analog signals (e.g., amplification, filtering, frequencyupconverting), and then generates a downlink signal suitable for atransmission on a radio channel. Subsequently, the downlink signal istransmitted to the user equipment via the antenna 130.

In the configuration of the user equipment 110, the receiving antenna135 receives the downlink signal from the base station and then providesthe received signal to the receiver 140. The receiver 140 adjusts thereceived signal (e.g., filtering, amplification and frequencydownconverting), digitizes the adjusted signal, and then obtainssamples. The symbol demodulator 145 demodulates the received pilotsymbols and then provides them to the processor 155 for channelestimation.

The symbol demodulator 145 receives a frequency response estimated valuefor downlink from the processor 155, performs data demodulation on thereceived data symbols, obtains data symbol estimated values (i.e.,estimated values of the transmitted data symbols), and then provides thedata symbols estimated values to the received (Rx) data processor 150.The received data processor 150 reconstructs the transmitted trafficdata by performing demodulation (i.e., symbol demapping, deinterleavingand decoding) on the data symbol estimated values.

The processing by the symbol demodulator 145 and the processing by thereceived data processor 150 are complementary to the processing by thesymbol modulator 120 and the processing by the transmitted dataprocessor 115 in the base station 105, respectively.

In the user equipment 110 in uplink, the transmitted data processor 165processes the traffic data and then provides data symbols. The symbolmodulator 170 receives the data symbols, multiplexes the received datasymbols, performs modulation on the multiplexed symbols, and thenprovides a stream of the symbols to the transmitter 175. The transmitter175 receives the stream of the symbols, processes the received stream,and generates an uplink signal. This uplink signal is then transmittedto the base station 105 via the antenna 135.

In the base station 105, the uplink signal is received from the userequipment 110 via the antenna 130. The receiver 190 processes thereceived uplink signal and then obtains samples. Subsequently, thesymbol demodulator 195 processes the samples and then provides pilotsymbols received in uplink and a data symbol estimated value. Thereceived data processor 197 processes the data symbol estimated valueand then reconstructs the traffic data transmitted from the userequipment 110.

The processor 155/180 of the user equipment/base station 110/105 directsoperations (e.g., control, adjustment, management, etc.) of the userequipment/base station 110/105. The processor 155/180 may be connectedto the memory unit 160/185 configured to store program codes and data.The memory 160/185 is connected to the processor 155/180 to storeoperating systems, applications and general files.

The processor 155/180 may be called one of a controller, amicrocontroller, a microprocessor, a microcomputer and the like. And,the processor 155/180 may be implemented using hardware, firmware,software and/or any combinations thereof. In the implementation byhardware, the processor 155/180 may be provided with such a deviceconfigured to implement the present invention as ASICs (applicationspecific integrated circuits), DSPs (digital signal processors), DSPDs(digital signal processing devices), PLDs (programmable logic devices),FPGAs (field programmable gate arrays), and the like.

Meanwhile, in case of implementing the embodiments of the presentinvention using firmware or software, the firmware or software may beconfigured to include modules, procedures, and/or functions forperforming the above-explained functions or operations of the presentinvention. And, the firmware or software configured to implement thepresent invention is loaded in the processor 155/180 or saved in thememory 160/185 to be driven by the processor 155/180.

Layers of a radio protocol between a user equipment/base station and awireless communication system (network) may be classified into 1st layerL1, 2nd layer L2 and 3rd layer L3 based on 3 lower layers of OSI (opensystem interconnection) model well known to communication systems. Aphysical layer belongs to the 1st layer and provides an informationtransfer service via a physical channel. RRC (radio resource control)layer belongs to the 3rd layer and provides control radio resourcedbetween UE and network. A user equipment and a base station may be ableto exchange RRC messages with each other through a wirelesscommunication network and RRC layers.

In the present specification, although the processor 155/180 of the userequipment/base station performs an operation of processing signals anddata except a function for the user equipment/base station 110/105 toreceive or transmit a signal, for clarity, the processors 155 and 180will not be mentioned in the following description specifically. In thefollowing description, the processor 155/180 can be regarded asperforming a series of operations such as a data processing and the likeexcept a function of receiving or transmitting a signal without beingspecially mentioned.

The present invention proposes an information utilization method forself-interference cancellation (Self-IC) in a full-duplex radio (FDR)system. Particularly, the invention discloses a method of storinginformation used in previous Self-IC for the purpose of reusing andreprocessing the stored information for current Self-IC. Consideringthat data to be transmitted is known in the FDR system, it is possibleto implement a method of performing Self-IC using existing informationsuch as self-interference (SI) or self-interference channel gain (orself-channel gain) when hybrid automatic repeat request (HARQ) isreceived. More particularly, the invention proposes a method forobtaining additional information for Self-IC using HARQ indicator (HI)information of both transmitting and receiving ends and determininginformation used for the Self-IC.

FIG. 3 is a conceptual diagram of self-interference (SI) and Tx/Rx linksin an FDR communication environment.

Referring to FIG. 3, the SI can be divided into direct interference,which is caused when a signal transmitted from a transmit (Tx) antennais received at an Rx antenna of the same device without pathattenuation, and reflected interference, which is caused when a signaltransmitted from a Tx antenna is reflected on a surrounding object andthen received at an Rx antenna of the same device. In addition, thestrength of the SI is extremely higher than that of a desired signal dueto a physical distance difference. Thus, the SI should be cancelled forefficient operation of the FDR system.

Table 1 shows requirements of the Self-IC in accordance with a maximumTx power of a device for the efficient operation of the FDR system.

TABLE 1 Self-IC requirements when the FDR is applied to a mobilecommunication system (BW = 20 MHz) Receiver Max. Tx Thermal Noise.Thermal Noise Self-IC Target Node Type Power (P_(A)) (BW = 20 MHz)Receiver NF Level (P_(A)-TN-NF) Macro 46 dBm −101 dBm 5 dB −96 dBm 142dB eNB (for eNB) Pico eNB 30 dBm 126 dB Femto 23 dBm 119 dB eNB, WLAN APUE 23 dBm 9 dB −92 dBm 115 dB (for UE)

Referring to Table 1, it may be noted that to effectively operate theFDR system in a 20-MHz BW, a UE needs 119-dBm Self-IC performance. Athermal noise value may be changed to N_(0,BW)=−174 dBm+10×log₁₀(BW) tothe BW of a mobile communication system. In Table 3, the thermal noisevalue is calculated on the assumption of a 20-MHz BW. In relation toTable 3, for Receiver Noise Figure (NF), a worst case is consideredreferring to the 3GPP specification requirements. Receiver Thermal NoiseLevel is determined to be the sum of a thermal noise value and areceiver NF in a specific BW.

Types of Self-IC Schemes and Methods for Applying the Self-IC Schemes

FIG. 4 is a view illustrating positions at which three Self-IC schemesare applied, in a Radio Frequency (RF) Tx and Rx end (or an RF frontend) of a device. Now, a brief description will be given of the threeSelf-IC schemes.

Antenna Self-IC:

Antenna Self-IC is a Self-IC scheme that should be performed first ofall Self-IC schemes. SI is cancelled at an antenna end. Most simply,transfer of an SI signal may be blocked physically by placing asignal-blocking object between a Tx antenna and an Rx antenna, thedistance between antennas may be controlled artificially, using multipleantennas, or a part of an SI signal may be canceled through phaseinversion of a specific Tx signal. Further, a part of an SI signal maybe cancelled by means of multiple polarized antennas or directionalantennas.

Analog Self-IC:

Interference is canceled at an analog end before an Rx signal passesthrough an Analog-to-Digital Convertor (ADC). An SI signal is canceledusing a duplicated analog signal. This operation may be performed in anRF region or an Intermediate Frequency (IF) region. SI signalcancellation may be performed in the following specific method. Aduplicate of an actually received SI signal is generated by delaying ananalog Tx signal and controlling the amplitude and phase of the delayedTx signal, and subtracted from a signal received at an Rx antenna.However, due to the analog signal-based processing, the resultingimplementation complexity and circuit characteristics may causeadditional distortion, thereby changing interference cancellationperformance significantly.

Digital Self-IC:

Interference is canceled after an Rx signal passes through an ADC.Digital Self-IC covers all IC techniques performed in a baseband region.Most simply, a duplicate of an SI signal is generated using a digital Txsignal and subtracted from an Rx digital signal. Or techniques ofperforming precoding/postcoding in a baseband using multiple antennas sothat a Tx signal of a UE or an eNB may not be received at an Rx antennamay be classified into digital Self-IC. However, since digital Self-ICis viable only when a digital modulated signal is quantized to a levelenough to recover information of a desired signal, there is a need forthe prerequisite that the difference between the signal powers of adesigned signal and an interference signal remaining after interferencecancellation in one of the above-described techniques should fall intoan ADC range, to perform digital Self-IC.

FIG. 5 is a block diagram of a Self-IC device in a proposedcommunication apparatus in an OFDM communication environment based onFIG. 4.

While FIG. 5 shows that digital Self-IC is performed using digital SIinformation before Digital to Analog Conversion (DAC) and after ADC, itmay be performed using a digital SI signal after Inverse Fast FourierTransform (IFFT) and before Fast Fourier Transform (FFT). Further,although FIG. 5 is a conceptual view of Self-IC though separation of aTx antenna from an Rx antenna, if antenna Self-IC is performed using asingle antenna, the antenna may be configured in a different manner fromin FIG. 5. A functional block may be added to or removed from an RF Txend and an RF Rx end shown in FIG. 5 according to a purpose.

Signal Modeling in the FDR System

A signal received at a device (e.g., UE, BS, etc.) in the FDR system canbe modeled as shown in Equation 1.

$\begin{matrix}{{{y\lbrack n\rbrack} = {{\sum\limits_{{k = 1},\ldots \;,K}^{\;}{{h_{{SI},k}\lbrack n\rbrack}{x_{SI}^{k}\lbrack n\rbrack}}} + {{h_{D}\lbrack n\rbrack}{x_{D}\lbrack n\rbrack}} + {z\lbrack n\rbrack}}},} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$

In Equation 1, x_(SI)[n] indicates data transmitted from an RFtransmitter of the device, h_(SI)[n] indicates a self-interferencechannel (self-channel) gain of the data transmitted from the RFtransmitter, x_(D)[n] indicates data that an RF receiver of the devicedesires to receive, h_(D)[n] indicates a desired channel gain of thedata that the RF receiver desires to receive, and z[n] indicatesAdditive White Gaussian Noise (AWGN). In this case, k may be consideredto have a value of 5 or 7 (i.e., k=5 or 7).

For the above-described analog or digital Self-IC, it is necessary toestimate the self-interference channel (self-channel). In this case,after completion of the Self-IC using a gain of the estimated analogand/or digital self-interference channel, ĥ_(SI,k) [n], for k=1, . . . ,K, the received signal of the device can be expressed as shown inEquation 2.

$\begin{matrix}{{y_{{Self}\text{-}{IC}}\lbrack n\rbrack} = {{{h_{D}\lbrack n\rbrack}{x_{D}\lbrack n\rbrack}} + {\sum\limits_{{k = 1},\; \ldots \;,K}^{\;}{\underset{ResidualSI}{( {{h_{{SI},k}\lbrack n\rbrack} - {{\hat{h}}_{{SI},k}\lbrack n\rbrack}} )}{x_{SI}^{k}\lbrack n\rbrack}}} + {{z\lbrack n\rbrack}.}}} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack\end{matrix}$

When the received signal is decoded using the estimated gain of thedescribed channel, ĥ_(D) [n], the received signal can be expressed asshown in Equation 3.

$\begin{matrix}\begin{matrix}{\frac{{{\hat{h}}_{D}^{*}\lbrack n\rbrack}{y_{{Self}\text{-}{IC}}\lbrack n\rbrack}}{{{{\hat{h}}_{D}\lbrack n\rbrack}}^{2}} = {{\frac{{{\hat{h}}_{D}^{*}\lbrack n\rbrack}{h_{D}\lbrack n\rbrack}}{{{{\hat{h}}_{D}\lbrack n\rbrack}}^{2}}{x_{D}\lbrack n\rbrack}} + \frac{{{\hat{h}}_{D}^{*}\lbrack n\rbrack}{z^{\prime}\lbrack n\rbrack}}{{{{\hat{h}}_{D}\lbrack t\rbrack}}^{2}}}} \\{{= {{x_{D}\lbrack n\rbrack} + \frac{{{\hat{h}}_{D}^{*}\lbrack n\rbrack}{e\lbrack n\rbrack}}{{{{\hat{h}}_{D}\lbrack n\rbrack}}^{2}} + \frac{{{\hat{h}}_{D}^{*}\lbrack n\rbrack}{z^{\prime}\lbrack n\rbrack}}{{{{\hat{h}}_{D}\lbrack n\rbrack}}^{2}}}},}\end{matrix} & \lbrack {{Equation}\mspace{14mu} 3} \rbrack\end{matrix}$

In Equation 3,

${z^{\prime}\lbrack n\rbrack} = {{\sum\limits_{{k = 1},\; \ldots \;,K}^{\;}{( {{h_{{SI},k}\lbrack n\rbrack} - {{\hat{h}}_{{SI},k}\lbrack n\rbrack}} ){x_{SI}^{k}\lbrack n\rbrack}}} + {z\lbrack n\rbrack}}$

and e[n]=ĥ_(D) [n]−H_(D)[n].

According to the initial digital self-interference cancellationtechnique, linear components of the interference signal are modeled fordigital self-interference cancellation. In recent years, efforts aremade to implement a digital self-interference cancellation technique ofusing not only linear components of interference signal information butalso non-linear components of the interference signal information forfeasible operation of the FDR system. As shown in Equation 1, linear andnon-linear components of SI information may be determined by transmitteddata and an interference channel gain of the transmitted data.Therefore, interference signal information needs to be calculated andupdated every transmission. However, if an SI signal including linearand nonlinear components is calculated in real time whenevertransmission is performed, it may increase the amount of calculation andcomplexity. Therefore, a method for reducing the complexity of thedigital self-interference cancellation while efficiently operating thesystem needs to be developed.

FIG. 6 is a diagram illustrating a procedure for self-interferencecancellation performed by devices (e.g., user equipment, base station,etc.) in the FDR system.

Referring to FIG. 6, a device initiates FDR operation [S610] and cancelsan SI signal using the antenna Self-IC scheme and analog Self-IC scheme[S620]. After cancelling the SI signal by applying the antenna Self-ICscheme and analog Self-IC scheme, the device can obtain the signal ofEquation 1,

${{y\lbrack n\rbrack} = {{\sum\limits_{{k = 1},\ldots \;,K}^{\;}{{h_{{SI},k}\lbrack n\rbrack}{x_{SI}^{k}\lbrack n\rbrack}}} + {{h_{D}\lbrack n\rbrack}{x_{D}\lbrack n\rbrack}} + {z\lbrack n\rbrack}}},.$

Next, the device can generate a digital SI signal from the signal ofEquation 1 [S630] and then obtain the signal of Equation 2 by performingthe digital Self-IC using the generated digital SI signal [S640]. Afterperforming the digital Self-IC on a block which is expected to contain adesired signal (i.e., a desired signal detection block), the device candetect the desired signal shown in Equation 3 through decoding [S650].After detection of the desired signal, the device can terminate the FDRoperation [S660].

FIG. 7 is a diagram illustrating another procedure for self-interferencecancellation (Self-IC) different from that of FIG. 6.

Referring to FIG. 7, steps S710 to S750 are similar to the steps S610 toS650 of FIG. 6. However, the procedure of FIG. 7 is different from thatof FIG. 6 in that a block unit for regenerating a digital SI signal andstoring the regenerated digital SI signal in a memory unit can be addedto an RF chain (or RF end) and used for the Self-IC. In the FDR system,if the same data is retransmitted according to a retransmission requestfrom a UE or BS that currently performs communication, a signalidentical to the existing SI signal may be received at an RF receiver asan interference signal. Thus, if the interference signal used in thelast or previous digital Self-IC or a reconfigured SI signal is reused,it may reduce or eliminate complexity in generating a new SI signal.That is, before the RF transmitter retransmits the identical signal, thedevice detects the desired signal that the RF receiver desires toreceive [S750]. Thereafter, the device regenerates the digital SI signaland then stores it in the memory unit [S760]. The stored digital SIsignal can be used for cancelling interference that occurs when the samedata is retransmitted according to the retransmission request.

Meanwhile, signal detection performance significantly depends onaccuracy of an estimated SI channel (ĥ_(SI,k)[n]) and a desired channel(signal) (ĥ_(D) [n]). That is, the success or failure of the Self-IC canbe determined according to whether the final received signal issuccessfully detected or not. Table 2 shows a relationship between thesuccess or failure of the Self-IC and the success or failure ofdetecting the received signal (number of cases according to the successor failure of Self-IC and the success or failure of detecting thereceived signal).

TABLE 2 Success of Self-IC Failure of Self-IC Success of detecting Case1 None received signal Failure of detecting Case 2 Case 3 receivedsignal

In Table 2, the case 1 is a case in which the device successfullyreceives the desired signal after completion of the digital Self-IC, thecase 2 is a case in which in spite of the successful digital Self-IC,the device fails to detect the received signal due to erroneousestimation of the desired channel or a low-quality link, and the case 3is a case in which due to the failure of the Self-IC, the device failsto detect the received signal. In case of the failure of the Self-IC,since the strength of the interference signal is extremely higher thanthat of the received signal, it is determined that the device cannotdetect the received signal. In FIG. 8, a particular procedure forregenerating a digital SI signal and storing the regenerated digital SIsignal in a memory unit based on the above-described three cases.

FIG. 8 is a diagram illustrating a particular procedure for regeneratinga digital SI signal and storing the digital SI signal in a memory unitbased on the three cases shown in Table 2.

Basically, the success of detecting the received signal is highlyrelated to the success or failure of the Self-IC. In addition,considering that the previous (same) data is transmitted when a targetnode (e.g., a UE or BS) requests retransmission, a high Self-IC successrate is expected even though variables used in the previous Self-IC areused for the current Self-IC (or the variables used in the previousSelf-IC may not be changed or be modified). Therefore, the presentinvention proposes a method for performing the Self-IC based on ACK/NACKin response to transmitted and received signals.

For example, a BS transmits, to a UE, an HARQ indicator (HI) includingan ACK/NACK signal in response to a signal transmitted from the UEthrough a physical hybrid-ARQ indicator channel (PHICH) and the UEreceives the HI [S810] (On the other hand, the UE may transmit ACK/NACKinformation through a physical uplink control channel (PUCCH)). The UEdetermines whether the HI information received from the BS indicates ACKor NACK [S820]. If it is determined that the HI information indicatesthe ACK, the UE can discard the previously generated digital SIinformation with respect to the transmitted signal to which the responseis the ACK [S830]. On the other hand, if it is determined that the HIinformation indicates the NACK, the UE determines whether the previouslydesired received signal is decoded [S840]. That is, for example, if theUE receives, from the BS, HI information corresponding to a NACK signalin response to a signal transmitted in a subframe n, the UE needs todetermine whether a signal received in the subframe n is decoded or not.This corresponds to the case 1 of Table 2. If the received signal isdecoded, the UE regenerate the digital SI signal and stores theregenerated digital SI signal in the memory unit [S850]. On thecontrary, if the received signal is not decoded, the UE determineswhether the Self-IC is successful [S860]. If the Self-IC is successful,this corresponds to the case 2 of Table 2. The UE regenerates thedigital SI signal and then stores the regenerated digital SI signal inthe memory unit. If the Self-IC is not successful, the UE generates adigital SI signal together with a partial SI signal [S870]. Theabove-described Self-IC method can be applied to not only a UE but alsoall wireless communication devices using the FDR mode such as a BS.Moreover, to secure a capacity of the memory, the UE can determinewhether to continuously store SI signals as shown in FIG. 9. That is,the UE may determine whether to store the SI signals based on the HIinformation received from the BS.

FIG. 9 is a diagram for explaining a procedure for self-interferencecancellation proposed in the present invention.

Referring to FIG. 9, a device (e.g., UE) regenerate the digital SIsignal [S910] and then the regenerated digital SI signal in the memoryunit [S920]. Thereafter, the device determines whether HI informationreceived from a target node (e.g., BS) indicates ACK or NACK [S930]. Ifit is determined that the HI information indicates the ACK, the devicediscards SI information with respect to the transmitted signal to whichthe response is the ACK [S940].

FIG. 10 is a block diagram of a device for performing the proposedmethod based on FIG. 5.

To compensate and store an SI signal used for a digital Self-IC scheme,a controller 1010 with a memory block is installed in a cancellationblock. Operation of the controller 1010 with the memory block will bedescribed in detail.

Embodiment 1: Method for Storing a Previously Used SI Signal in theMemory without any Change

According to the embodiment 1 of the present invention, a BS/UE stores apreviously estimated digital SI signal (or an SI signal of a digitalend) (e.g., residual SI signal after analog self IC) for the purpose ofreusing a digital SI signal. The BS/UE stores the signal in the memoryto reuse an estimated SI signal,

${{{\hat{SI}}_{1}\lbrack n\rbrack} = {\sum\limits_{{k = 1},\ldots \;,K}^{\;}{{{\hat{h}}_{{SI},k}\lbrack n\rbrack}{x_{SI}^{k}\lbrack n\rbrack}}}},$

which is used to obtain Equation 2. In this case, instead of separatelystoring an estimated SI channel gain (self-channel gain), ĥ_(SI,k)[n]and transmitted data information, x_(SI)[n], the BS/UE can store acompleted digital SI signal obtained by adding a product of the Tx dataand the estimated SI channel gain (self-channel gain). In addition, theBS/UE can discard the stored digital SI signal after receiving an ACKsignal received from a target node (e.g., UE/BS) after elapse of apredetermined time. Alternatively, the BS/UE can maintain the storeddigital SI signal after receiving an NACK signal.

Embodiment 2: Method for Storing a Previously Used SI Signal in theMemory after Eliminating Encoded Tx Data Portion from the SI Signal

According to the embodiment 2 of the present invention, it is proposedthat the BS/UE stores an SI signal estimated by subtracting informationon decoded desired received data from the received signal for thepurpose of reusing the digital SI signal. After successfully decodingthe received signal, the BS/UE can generate the digital SI signal to bereused by using the decoded received data and an estimated desiredchannel gain. Generally, non-linear characteristics frequently occur inhardware due to the high strength of the SI signal and it maysignificantly affect a value of residual SI,

${\sum\limits_{{k = 1},\; \ldots \;,K}^{\;}{( {{h_{{SI},k}\lbrack n\rbrack} - {{\hat{h}}_{{SI},k}\lbrack n\rbrack}} ){x_{SI}^{k}\lbrack n\rbrack}}},$

which is created by a deviation of the SI signal. Thus, a method forreducing a deviation is also proposed. The new SI signal obtained bysubtracting the decoded received data from the received signal can beexpressed as shown in Equation 4.

$\begin{matrix}{{{\hat{SI}}_{Sub}\lbrack n\rbrack} = {{{y\lbrack n\rbrack} - {{h_{D}\lbrack n\rbrack}{x_{D}\lbrack n\rbrack}}} = {{\sum\limits_{{k = 1},\ldots \;,K}^{\;}{{h_{{SI},k}\lbrack n\rbrack}{x_{SI}^{k}\lbrack n\rbrack}}} + {( {{h_{D}\lbrack n\rbrack} - {{\hat{h}}_{D}\lbrack n\rbrack}} ){x_{D}\lbrack n\rbrack}} + {{z\lbrack n\rbrack}.}}}} & \lbrack {{Equation}\mspace{14mu} 4} \rbrack\end{matrix}$

The digital SI signal stored in the memory of the embodiment 1 isexpressed as ŜI₁[n] and the digital SI signal stored in the memory ofthe embodiment 2 is expressed as ŜI_(sub)[n]. Since the signal ŜI_(sub)[n] contains even non-estimated non-linear components unlike the digitalSI signal ŜI₁[n] stored in the memory of the embodiment 1, it cancontain not only an increase in Tx power but also complex non-linearcomponents of SI occurring in the MIMO FDR system. In addition, sincecalculation complexity of ĥ_(D)[n]x_(D)[n] is significantly lower thanthat of the SI signal, it is possible to generate a new SI signal inwhich the complex non-linear components are reflected without an immenseincrease in the complexity. An updated SI signal obtained by combiningthe SI signal that reflects the non-linear components obtained inEquation 2 and the digital SI signal ŜI₁[n] of the embodiment 1 can beexpressed as shown in Equation 5.

ŜI ₂ [n]=α×ŜI ₁ [n]+(1−α)×ŜI _(Sub) [n],  [Equation 5]

In Equation 5, α is a value for determining a ratio of a previouslyestimated SI value to an SI value estimated by reflecting statisticalcharacteristics. If α is 1, the SI value of the embodiment 1 is equal tothat of the embodiment 2. The value of α is determined according towhether the Self-IC is successful and thus, it can be changed. Thereference for determining α can be configured as follows. If a deviceoperating in the FDR mode is fixed like a BS and located at a placewithout scattering, α may be set to 1 because there is no SI channelvariation between store and transmission times. On the contrary, if thedevice operating in the FUR mode moves like a UE or located at a placewith scattering, α may be set to have a value less than 1 (e.g., 0.5)because the SI channel is significantly changed between the store andtransmission times. Moreover, if a new SI channel is made due to asignificant change in the surrounding environment, the previously storedSI channel information may cause a negative effect on the Self-IC. Thus,if a channel value obtained by performing subtraction after decoding bysetting α to 0 is used, it is possible to obtain better Self-IC results.

Embodiment 3: Method for Storing a Previously Used SI Signal in theMemory after Eliminating Encoded Tx Data Portion from the SI Signal

According to the embodiment 3 of the present invention, it is proposedthat the BS/UE estimates the previous SI signal in consideration ofstatistical characteristics of the received signal for the purpose ofreusing the digital SI signal. After successfully decoding the receivedsignal, the BS/UE can generate the digital SI signal to be reused byusing the decoded received data, the estimated SI channel gain(self-channel gain), and statistical characteristics of the desiredchannel gain. A minimum mean square error (MMSE) filter value can becalculated as shown in Equation 6 using x_(SI)[n] corresponding toinformation known by transmission or decoding to a transmitter, powerstrength P_(x) _(SI) of x_(D)[n], and distribution values σ_(h) _(SI) ²and σ_(h) _(D) ² between P_(x) _(D) and the estimated self-channel gainand desired-channel gain.

$\begin{matrix}{{W_{MMSE} = \frac{P_{X_{SI}}\sigma_{h_{SI}}^{2}}{{P_{X_{SI}}\sigma_{h_{SI}}^{2}} + {P_{X_{D}}\sigma_{h_{D}}^{2}} + \sigma_{z}^{2}}},} & \lbrack {{Equation}\mspace{14mu} 6} \rbrack\end{matrix}$

In Equation 6, σ_(z) ² indicates a noise variance. If the MMSE filterfactor calculated in Equation 6 is multiplied with the received signal,it is possible to obtain the SI signal in which the statisticalcharacteristics are reflected. The SI signal can be expressed as shownin Equation 7.

ŜI _(MMSE) [n]=W _(MMSE) y[n].  [Equation 7]

The updated SI signal obtained by combining the SI signal of Equation 7that reflects the statistical characteristics and the signal of theembodiment 1 can be expressed as shown in Equation 8.

ŜI ₃ [n]=α×ŜI ₁ [n]+(1−α)×ŜI _(MMSE) [n],  [Equation 8]:

In Equation 8, α is a value for determining a ratio of a previouslyestimated SI signal value to an SI signal value estimated by reflectingthe statistical characteristics. If α is 1, the SI signal value of theembodiment 3 is equal to that of the embodiment 1. The value of α isdetermined according to whether the Self-IC is successful and thus, itcan be changed. The reference for determining α can be configured asfollows. If a device operating in the FDR mode is fixed like a BS andlocated at a place without scattering, α may be set to 1 because thereis no SI channel variation between store and transmission times. On thecontrary, if the device operating in the FDR mode moves like a UE orlocated at a place with scattering, α may be set to have a value lessthan 1 (e.g., 0.5) because the SI channel is significantly changedbetween the store and transmission times. Moreover, if a new SI channelis made due to a significant change in the surrounding environment, thepreviously stored SI channel information may cause a negative effect onthe Self-IC. Thus, if a statistical channel value is used after settingα to 0, it is possible to obtain better Self-IC results.

Embodiment 4: Method for Using the SI Signal Stored in the Memory inAccordance with the Embodiments 1 to 3 in the Case of Non-Adaptive HARQ

According to the embodiment 4 of the present invention, it is proposedthat the BS/UE performs the digital Self-IC by reusing the stored SIsignal when the BS/UE retransmits the same data according to anon-adaptive HARQ request. Specifically, according to the embodiment 4,if the BS/UE needs to retransmit the same data due to the non-adaptiveHARQ request after elapse of a predetermined time (in case of uplink(UL), the predetermined time may be set to 8 subframes, i.e., theretransmission may be performed in a subframe (n+8), whereas in case ofdownlink (DL), it may be changed), the BS/UE can skip the procedure forcreating the new SI signal for the Self-IC and perform the Self-ICthrough a digital Self-IC block using ŜI₁[n]ŜI₂[n] or ŜI₃[n] stored inthe memory in accordance with the embodiments 1 to 3 because a change inthe SI channel gain depending on time is relatively smaller than that inthe desired channel when the BS/UE operates in the FUR mode.

In detail, the BS/UE determines whether a signal received in a subframen before the retransmission is decoded by using HARQ informationtransmitted from a target node (UE/BS). That is, in the case of the dataretransmission, the BS/UE reuses the SI signal ŜI₁[n]ŜI₂[n] or ŜI₃[n] inthe subframe, which is stored in the memory, for the Self-IC only whensuccessfully decoding the received signal.

For example, when ŜI₁[n] is reused in the case of the dataretransmission, signal modeling can be implemented as follows. If thesame data is transmitted in a subframe (n+n_(R)) according to theretransmission request from the target UE/BS, the received signal can bemodeled in the FUR system as shown in Equation 9.

$\begin{matrix}{{{y\lbrack {n + n_{R}} \rbrack} = {{\sum\limits_{{k = 1},\ldots \;,K}^{\;}{{h_{{SI},k}\lbrack {n + n_{R}} \rbrack}{x_{{SI},{{NA}\text{-}{HARQ}}}^{k}\lbrack {n + n_{R}} \rbrack}}} + {{h_{D}\lbrack {n + n_{R}} \rbrack}{x_{D}\lbrack {n + n_{R}} \rbrack}} + {n\lbrack {n + n_{R}} \rbrack}}},} & \lbrack {{Equation}\mspace{14mu} 9} \rbrack\end{matrix}$

In Equation 9, x_(SI) ₁ _(NA-HARQ)[n+n_(R)] indicates data transmittedby the BS/UE in the subframe (n+n_(R)) in a non-adaptive HARQ manneraccording the retransmission request. In addition, since the data x_(SI)₁ _(NA-HARQ)[n+n_(R)] is transmitted using the same modulation andcoding scheme (MCS) level and resource blocks (RBs) as those used in theprevious data transmission, the data x_(SI) ₁ _(NA-HARQ)[n+n_(R)] isidentical to the data x_(SI)[n] transmitted in the subframe n, i.e.,x_(SI) ₁ _(NA-HARQ)[n+n_(R)]=x_(SI)[n] (since simple retransmission isperformed, the transmitted data is the same).

As described above, the BS/UE performs the Self-IC on the subframe(n+n_(R)) through the digital Self-IC block by reusing the digital SIsignal information ŜI₁[n] that is estimated in the subframe n throughthe digital Self-IC block. In this case, a received signal passingthrough the digital Self-IC step can be expressed as shown in Equation10.

$\begin{matrix}\begin{matrix}{{y_{{Self}\text{-}{IC}}\lbrack {n + n_{R}} \rbrack} = {{\sum\limits_{{k = 1},\ldots \;,K}{{h_{{SI},k}\lbrack {n + n_{R}} \rbrack}{x_{{SI},{{NA}\text{-}{HARQ}}}^{k}\lbrack {n + n_{R}} \rbrack}}} -}} \\{{{{{SI}_{1}\lbrack n\rbrack} + {{h_{D}\lbrack {n + n_{R}} \rbrack}{x_{D}\lbrack {n + n_{R}} \rbrack}} + {n\lbrack {n + n_{R}} \rbrack}},}} \\{= {{{h_{D}\lbrack {n + n_{R}} \rbrack}{x_{D}\lbrack {n + n_{R}} \rbrack}} +}} \\{{\sum\limits_{{k = 1},\; \ldots \;,K}^{\;}( {{h_{{SI},k}\lbrack {n + n_{R}} \rbrack} - {h_{{SI},k}\lbrack n\rbrack}} )}} \\{{{x_{{SI},{{NA}\text{-}{HARQ}}}^{k}\lbrack {n + n_{R}} \rbrack} + {{n\lbrack {n + n_{R}} \rbrack}.}}}\end{matrix} & \lbrack {{Equation}\mspace{14mu} 10} \rbrack\end{matrix}$

It can be seen that a residual SI signal in Equation 10 has a valuedifferent from that of the residual SI signal in Equation 2. However, inthe environment in which the SI channel is not or slightly changeddepending on time, since a difference between

$\sum\limits_{{k = 1},\ldots \;,K}{{h_{{SI},k}\lbrack {n + n_{R}} \rbrack}{x_{{SI},{{NA}\text{-}{HARQ}}}^{k}\lbrack {n + n_{R}} \rbrack}\mspace{14mu} {and}}$$\sum\limits_{{k = 1},\ldots \;,K}^{\;}{{h_{{SI},k}\lbrack n\rbrack}{x_{SI}^{k}\lbrack n\rbrack}}$

is small enough to be handled by the digital Self-IC, the successfulprevious Self-IC results can be reused through the digital SIinformation stored in the memory, thereby achieving excellent Self-ICperformance in the case of the retransmission.

In addition, according to a sub-embodiment (embodiment 4-1) of theembodiment 4, it is proposed that when intending to perform theretransmission, the BS/UE operating in the FDR mode performs theretransmission based on the non-adaptive HARQ using the same MCS leveland RBs as those used in the previous transmission and reception basedon chase combining for above-mentioned reasons.

Moreover, according to another sub-embodiment (embodiment 4-2) of theembodiment 4, when intending to perform the retransmission, the BS/UEoperating in the FDR mode can store the digital SI signal information inthe memory in each or all of the 8 subframes for above-mentionedreasons.

Furthermore, according to a further sub-embodiment (embodiment 4-3) ofthe embodiment 4, when performing a transmission time interval (TTI)bundling transmission method, the BS/UE operating in the FDR mode cancontinuously use the SI signal information used in the previoustransmission for above-mentioned reasons. Considering that the TTIbundling method is used to transmit ACK/NACK information at once for thepurpose of reducing feedback overhead, the BS/UE can continuously usethe SI signal information and SI channel information, which is stored inthe memory for the retransmission.

Embodiment 5: Method Performed by an FDR Device for Determining WhetherSelf-IC is Successful

In the above embodiments, it has been described how the FDR devicedetermines whether the Self-IC is successful. In the present embodiment,it is described how the FDR device determines whether the Self-IC issuccessful based on a window-based control signal when the FDR devicefails to decode the received signal.

In the case 2 of Table 2, a device fails to decode a received signal inspite of successful Self-IC. In general, if the device fails to decodethe received signal, the device cannot know whether the Self-IC issuccessful or not because the device cannot know which steps in thedecoding and Self-IC processes are problematic. However, in this case,the SI signal can be reused as follows.

According to the embodiment 5, it is proposed that the BS/UE determineswhether to use the previously used SI signal or SI channel byaccumulating or processing information on whether the received signal issuccessfully decoded before the retransmission during a predeterminedtime. If the SI channel gain is changed, the BS/UE operating in the FDRmode anticipates whether the SI channel gain is changed by accumulatingor processing the information on whether the received signal issuccessfully decoded before the retransmission during the predeterminedtime to compensate a change in the SI channel gain. Based on theanticipated results, the BS/UE determines whether to reuse the stored SIsignal (i.e., ŜI₁[n]ŜI₂[n] or ŜI₃[n]) or the SI channel gain(ĥ_(SI,k)[n], for k=1, . . . , K).

According to a sub-embodiment (embodiment 5-1) of the embodiment 5, whenthe UE operating in the FDR mode performs uplink transmission, it ispossible to accumulate HI information included in one PHICH or PHICHgroup during W subframes before the subframe n and use the accumulatedHI information to obtain information on whether the decoding issuccessful.

FIG. 11 illustrates an example in which success of self-interferencecancellation (Self-IC) is expected based on consecutive HI informationin accordance with the embodiment 5-1.

Referring to FIG. 11, if W is, for example, 6, it is possible to expectthe success of the Self-IC based on 6 consecutive pieces of ACKinformation before the subframe n.

FIG. 12 illustrates an example in which failure of self-interferencecancellation (Self-IC) is expected based on consecutive HI informationin accordance with the embodiment 5-1.

If the number of accumulated ACKs is less than a threshold, it ispossible to expect the failure of the Self-IC. As shown in FIG. 12, ifthe number of accumulated ACKs is equal to or less than 5 subframes, itis possible to expect the failure of the Self-IC.

According to another sub-embodiment (embodiment 5-2) of the embodiment5, when the UE operating in the FDR mode performs uplink transmission,it is possible to accumulate HI information included in one PHICH orPHICH group during W subframes including the subframe n and use theaccumulated HI information to obtain information on whether the decodingis successful.

FIG. 13 illustrates an example in which success of self-interferencecancellation (Self-IC) is expected based on consecutive HI informationin accordance with the embodiment 5-2.

As shown in FIG. 13, if W is, for example, 6, it is possible to expectthe success of the Self-IC based on 6 consecutive pieces of ACKinformation after the subframe n.

FIG. 14 illustrates an example in which failure of self-interferencecancellation (Self-IC) is expected based on consecutive HI informationin accordance with the embodiment 5-2.

As shown in FIG. 14, if the number of accumulated ACKs is less than athreshold, it is possible to expect the failure of the Self-IC. That is,if the number of ACKs accumulated during 6 subframes after the subframen is equal to or less than 5 subframes, it is possible to expect thefailure of the Self-IC.

According to a further sub-embodiment (embodiment 5-3) of the embodiment5, when the UE operating in the FDR mode performs uplink transmission,it is possible to accumulate HI information included in one PHICH orPHICH group during W subframes before and after the subframe n and usethe accumulated HI information to obtain information on whether thedecoding is successful.

FIG. 15 illustrates an example in which success of self-interferencecancellation (Self-IC) is expected based on consecutive HI informationin accordance with the embodiment 5-3.

As shown in FIG. 15, if W is, for example, 6, it is possible to expectthe success of the Self-IC based on 6 consecutive pieces of ACKinformation except the subframe n.

FIG. 16 illustrates an example in which failure of self-interferencecancellation (Self-IC) is expected based on consecutive HI informationin accordance with embodiment 5-3.

If the number of ACKs accumulated during 6 consecutive subframes exceptthe subframe n is less than a threshold, it is possible to expect thefailure of the Self-IC. For example, if the number of ACKs accumulatedduring the 6 consecutive subframes except the subframe n is equal to orless than 5 subframes as shown in FIG. 16, it is possible to expect thefailure of the Self-IC.

As described with the embodiment 5, whether the Self-IC is successfulcan be estimated based on the accumulated HI information. In addition,if it is determined that the Self-IC is successfully performed, it ispossible to reduce complexity in generating the SI signal to be used forthe Self-IC by reusing the SI signal as mentioned with reference to theembodiments 1 to 4.

Further, when the FDR device performs the retransmission afterdetermining that the Self-IC is successful based on the accumulated HIinformation as described above with reference to the embodiment 5, theFDR device may have been failed to perform the Self-IC. This is becauseinformation on the success of the Self-IC may not be accurate eventhough the accumulated HI information is used or the channel may bechanged at a time when the retransmission is performed. In this case,after determining that accuracy of the stored SI signal in accordancewith the embodiments 1 to 4 is low, the FDR device can discard theinformation stored in the memory and then perform estimation of aself-channel and reconfiguration of an SI signal.

The embodiments of the present invention described hereinabove arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in the embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obviousthat claims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentinvention or included as a new claim by subsequent amendment after theapplication is filed.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

INDUSTRIAL APPLICABILITY

A device capable of supporting an FDR scheme and performingself-interference signal cancellation according to the present inventioncan be industrially applied to various wireless communication systemsincluding the 3GPP LTE/LTE-A system.

What is claimed is:
 1. A method for performing self-interference signalcancellation by an apparatus supporting a full duplex communication(FDR) mode, the method comprising: transmitting a signal to a targetnode in a predetermined time interval; generating and storing a residualself-interference signal after cancelling an analog self-interferencesignal associated with the signal at a radio frequency (RF) end of theapparatus; receiving an acknowledgement/negative-acknowledgement(ACK/NACK) signal from the target node in response to the transmittedsignal; and determining whether to use the stored residualself-interference signal later based on the ACK/NACK signal.
 2. Themethod of claim 1, further comprising: when an ACK signal is receivedfrom the target node in response to the transmitted signal, determiningto discard the stored self-interference signal.
 3. The method of claim1, further comprising: when a NACK signal is received from the targetnode in response to the transmitted signal, determining whether a signalreceived in the predetermined time interval is successfully decoded. 4.The method of claim 3, further comprising: retransmitting the signal tothe target node; and when the signal received in the predetermined timeinterval is successfully decoded, using the stored residualself-interference signal in cancelling a digital self-interferencesignal associated with the retransmission.
 5. The method of claim 3,further comprising: retransmitting the signal to the target node; andwhen the signal received in the predetermined time interval is notsuccessfully decoded, determining whether self-interference cancellationis successful.
 6. The method of claim 5, wherein the success or failureof the self-interference cancellation is determined based on whether apredetermined number or more of consecutive ACK signals are receivedfrom the target node.
 7. The method of claim 6, further comprising: whenit is determined that the self-interference cancellation is successful,using the stored residual self-interference signal in cancelling adigital self-interference signal associated with the retransmission. 8.The method of claim 6, further comprising: when it is determined thatthe self-interference cancellation is not successful, discarding thestored residual self-interference signal.
 9. An apparatus for performingself-interference signal cancellation, the apparatus supporting a fullduplex communication (FDR) mode, the apparatus comprising: a transmittedconfigured to transmit a signal to a target node in a predetermined timeinterval; a radio frequency (RF) unit configured to generate and store aresidual self-interference signal after cancelling an analogself-interference signal associated with the signal; a receiverconfigured to receive an acknowledgement/negative-acknowledgement(ACK/NACK) signal from the target node in response to the transmittedsignal; and a processor configured to determine whether to use thestored residual self-interference signal later based on the ACK/NACKsignal.
 10. The device of claim 9, wherein when an ACK signal isreceived from the target node in response to the transmitted signal, theprocessor is configured to determine to discard the storedself-interference signal.
 11. The device of claim 9, wherein when thereceiver receives a NACK signal from the target node in response to thetransmitted signal, the processor is configured to determine whether asignal received in the predetermined time interval is successfullydecoded.
 12. The device of claim 11, wherein the transmitter isconfigured to retransmit the signal to the target node and wherein whenthe signal received in the predetermined time interval is successfullydecoded, the RF unit is configured to use the stored residualself-interference signal in cancelling a digital self-interferencesignal associated with the retransmission.
 13. The device of claim 11,wherein the transmitter is configured to retransmit the signal to thetarget node and wherein when the signal received in the predeterminedtime interval is not successfully decoded, the processor is configuredto determine whether self-interference cancellation is successful. 14.The device of claim 13, wherein the processor is configured to determinethe success or failure of the self-interference cancellation based onwhether a predetermined number or more of consecutive ACK signals arereceived from the target node.
 15. The device of claim 14, wherein whenit is determined that the self-interference cancellation is successful,the RF unit is configured to use the stored residual self-interferencesignal in cancelling a digital self-interference signal associated withthe retransmission.
 16. The device of claim 14, wherein when it isdetermined that the self-interference cancellation is not successful,the processor is configured to discard the stored residualself-interference signal.